Modern vehicle engines are called upon to drive an increasing number of accessories. In the conventional accessory drive system, the accessories are driven at a linear ratio which may differ from that of the speed of the engine but which may reach levels at which the accessory is inefficient and which may require accessory construction for strength and size which would not be necessary if driven in a different manner. Driving accessories at high speeds results in a substantial decrease in the efficiency of a vehicle because a substantial percentage of the output is required to drive the accessories, which can amount to about 30% of the engine horsepower at moderate vehicle speeds.
The problem of efficiency decrease becomes even more severe in some modern, low horsepower engines which must operate at relatively high speeds. The lack of efficiency of the system requires the use of more gasoline--a needless and serious waste of energy.
Various types of accessory drives have been proposed. Some are merely temperature responsive only, and thus intermittent, and not suitable for alternator or generator devices which must be driven continuously. Others are too expensive.